Free Astronomy Magazine January-February 2018

41 JANUARY-FEBRUARY 2018 SPACE CHRONICLES explore Webb’s full potential. Webb has a minimum scientific lifetime of five years, so the scientific commu- nity will have to rapidly learn to use its advanced capabilities. “We want the research community to be as sci- entifically productive as possible, as early as possible, which is why I am so pleased to be able to dedicate nearly 500 hours of director’s discre- tionary time to these ERS observa- tions,” said Sembach. One of the most widely anticipated areas of re- search by Webb is to study planets orbiting other stars. When such an exoplanet passes in front of its host star, starlight filters through the planet’s atmosphere, which absorbs certain colors of light depending on the chemical composition. Webb will measure this absorption, using its powerful infrared spectrographs, to look for the chemical fingerprints of the atmosphere’s gasses. Astrono- mers initially will train their gaze onto gaseous Jupiter-sized worlds like WASP-39b and WASP-43b be- cause they are easier targets on which to apply this technique. The results will help guide observing strategies for smaller, mostly rocky and more Earth-like super-Earths, where atmospheric composition may give hints of a planet’s poten- tial habitability. Webb also will peer into the distant universe, examining galaxies whose light has been stretched into in- frared wavelengths by the expan- sion of space. This infrared region is be- yond what Hubble can detect. Galaxy clusters are particularly rich sources of targets, since a cluster’s gravity can magnify light from more distant back- ground galaxies. DD-ERS observations will target regions of the sky already examined by Hubble’s Frontier Fields program, such as the galaxy clus- ter MACS J0717.5+3745. Webb data will comple- ment Hubble’s, giving as- tronomers new insights into these cornucopias of galaxies. Since Webb must remain shielded from sunlight, its field of view is limited to specific areas of the sky at certain times of year. As a result, the potential tar- gets listed above may shift depending on the launch date. More than 100 proposals for DD-ERS observations were submitted in August 2017. Of those, 13 pro- grams requesting 460 hours of telescope time were selected following review by panels of sub- ject matter experts and the STScI director. !